In order to understand why this is so, you have to understand that there are several very different kinds of fiber networks in the world – long-haul, distribution and last mile. Each kind of these networks is built in a very different way that doesn’t make them useful for the other two uses.
Consider long-haul fiber. This is the fiber that is built to connect cities and to stretch across the country and the world. The key to having an affordable long-haul fiber route is to carry each leg of the network as far as possible without stopping and having to repeat the signals. So generally long-haul fibers will only stop in major POPs in cities or wherever necessary along the way at repeater sites that are used to boost the signal.
I have a client who is sitting on one of the major east-west Interstates in the country. Every major long-haul carrier in the country is passing very near to him with owned or leased capacity on the long-haul route. My client was shocked when not one carrier would come off of the long-haul route to provide him with bandwidth. But it’s very costly to break into long-haul fibers, and every splice creates a little interference, and so long-haul providers are generally extremely reluctant to provide bandwidth anywhere except at established POPs along the fiber.
Distribution fiber is similar to long-haul fiber, but within local fiber networks. Distribution fibers are built to connect very specific points. The networks that cable companies build to get to their neighborhood nodes are a distribution network. So are networks built by telcos to reach DSL cabinets or networks built by cities to reach traffic signals and networks built by school boards to connect schools. These networks were generally built for the specific purpose of reaching those end points.
Distribution fiber routes share the same issue as the long-haul routes and the companies that own them are generally reluctant to break these routes along the way to connect to somebody that the network was not designed for. Certainly distribution fibers have very little use for providing service to many homes or businesses. There are generally not enough pairs of fiber in distribution routes, but more importantly they are not built with access points along the way.
The major characteristic of last mile fibers (and the one that makes them the most expensive) is the presence of many access points – using handholes, manholes, splice boxes or other ways to connect to the fiber where it’s needed. Providing these access points every few hundred feet adds a lot of cost to building fiber, and it’s very expensive, and often impossible to add access points after the fact to existing distribution fiber.
This is why I actually laughed out loud last year when I read about Comcast’s 2 gigabit product that they would sell to people who were close enough to their fiber. The Comcast fiber network is almost entirely a distribution network that connects from a central hub or ring to electronic boxes in neighborhoods known as nodes. When Comcast said a customer had to be close to their fiber, they didn’t mean that fiber had to be close the home, because distribution fiber passes lots of homes and businesses. They meant that a customer had to live close to a neighborhood node which are the only access points on a cable distribution network. Cable nodes are often placed where they aren’t an eyesore for homeowners and so I laughed because in most places hardly anybody lives close enough to a Comcast node to buy the touted 2 Gig service. In a city of 20,000 like mine I would be surprised if there are more than a dozen or two homes that would qualify to buy the Comcast service.
The same is true for most of the big ISPs. Verizon has built a lot of last mile fiber with FiOS and now CenturyLink is starting to do the same. But some of the other large companies like AT&T are very happy to talk about how close they are with fiber to homes and businesses without mentioning that the vast majority of that fiber is distribution fiber, which is close to worthless for providing fiber to homes and small businesses. This is not to say that companies like Comcast or AT&T don’t have any last mile fiber. They just don’t have very much of it and it’s generally limited to business parks or to greenfield neighborhoods where they’ve installed fiber instead of copper.